The ability to repair, reconstruct and replace components of the cardiovascular systems of humans and animals is dependent upon the availability of blood compatible materials. Thromboresistant materials are also required for the development of long-term metabolic support and monitoring systems, as well as for the development of various blood diagnosis, treatment and storage systems.
A large number of polymeric materials have been suggested and evaluated as blood contacting materials. Unfortunately, a variety of biological events has often resulted in the failure of these materials as antithrombogenic surface layers.
Surface-induced thrombosis is the result of the interplay between surface characteristics and blood stream components. Protein adsorption, cellular adhesion and activation, and the initiation of coagulation and complement pathways are the basic phenomena which control the extent of thrombus formation and, therefore, the performance of a blood-contacting material.
While the sequence leading to surface-induced thrombus formation involves a number of complex interacting pathways, each is initiated by the adsorption of blood plasma proteins by the introduced surface. Thus, a key requirement for antithrombogenic materials is that they have a low degree of blood protein adsorption, thereby preventing the initiation of the thrombogenic pathways. To this end, it is known that most surfaces which are rough, crystalline or glassy, and hydrophobic have high degrees of protein binding. On the other hand, surfaces which are smooth, amorphous, solvated by water, and non-electrolytic may have, but do not necessarily have, low blood-protein adsorptivities.
Although a wide variety of materials are currently used in blood-contacting applications, the results are often less than satisfactory. For example, artificial heart technology has been hampered by the inability to prevent thrombus formation induced by the implant surfaces. This has resulted in severe cerebral-vascular damage in a number of artificial heart recipients.
Thus, a need exists for a blood-contacting material which can reduce thrombus formation, has good physical properties, and is non-toxic when implanted.